Ternary alkali metal alloy



March 16, 1965 D. R. STERN ET AL 3,373,733

TERNARY ALKALI METAL gLLOY Filed July 16, 1962 2 Sheets-Sheet 1 425% N0 THE SYSTEM SODIUM-POTASSIUM-CESIUM 42.5%K

/ N VE N TORS DAVID R. STERN ROBERT D. STEWART A TTOR/VEY March 16, 1965 D. R. STERN ET AL 3,173,783

TERNARY ALKALI METAL ALLOY Filed July 16, 1962 2 Sheets-Sheet 2 CONDENSER 34 SUPERHEATER POWER PRODUCING MEANS l CONDENSER POWER 56 PRODUCING MEANS ATOMIC REACTOR IN VE NT OF:

DAVID R. STERN ROBERT D. STEWART "'5 ATTORNEY I' their methods of preparation.

ing to this invention.

United States Patent 3,173,783 TERNARY ALKALE METAL ALLOY David R. Stern, Fullerton, and Robert D. Stewart, La

Habra, Calirl, assiguors to American Potash & Chemical Corporation, Los Augeles, Califi, a corporation of Delaware Filed July 16, 1962, Ser. No. 209,864 3 Claims. (Cl. '75lt34) This invention relates to alkali metal alloys and to In particular, this invention relates to ternary cesium-potassium-sodium alloys and their methods of preparation.

Low melting, non-aqueous liquid heat transfer media which are liquid over a wide range of temperatures have long been sought. The present ternary alkali metal alloys provide a non-aqueous heat transfer medium which is liquid from about 73 C. to about 740 C. under atmospheric pressure. This alloy enjoys wide application in heat transfer, power cycles and in other applications where a heat carrying medium which is liquid over a wide temperature range is necessary. The present liquid ternary alloys are possessed of certain physical properties, for example, high heat capacity and thermal conductivity, which properties enhance the value of these alloys for use as heat carrying fluids in many applications.

Broadly, these alloys are comprised of a major amount of cesium, a minor amount of potassium and a small amount of sodium.

More particularly, ternary alloys of this invention, contain by weight from about 2 to about 7% sodium, from about 16 to about 36% potassium and from about 60 to about 80% cesium. A loys falling within this range of composition are liquid down to at least about 60 C. Between about 60 C. and about 73 C., a small amount of solid phase may appear in the liquid. The eutectic composition has a melting point of about -73 C.

Preferably, the alloys of this invention will contain from about 2.5 to about 4.5% sodium and from about 20 to about 31% potassium and from about 65 to about 77% cesium. These preferred alloys are liquid down to a temperature of at least about 70 C. Below this temperature down to about 73 C., most of the preferred alloy remains liquid but some solid phase is present.

Particularly, preferred alloys are those having the composition of about 2.8% to about 3.2% sodium and from about 20% to about 30% potassium and from about 67% to about 77% cesium. These preferred alloys are com pletely liquid down to a temperature of at least about 70 C. Our most preferred alloy is that falling within the range of composition of about 70-77% cesium, about 22.525.5% potassium and about 2.93.l% sodium. This alloy has a composition very close to the eutectic point and is substantially liquid down to a temperature of about 73 C.

The alloys of this invention are prepared by mechani cally mixing these metals at a temperature above their melting points in an inert environment. Mixing can be accomplished by agitation, stirring, or other conventional mechanical mixing procedures. Typical inert environments include anhydrous mineral oil or inert gas such as argon, neon, or the like.

FIG. 1 illustrates the phase diagram for the alloys of this invention.

FIG. 2 illustrates schematically one preferred embodiment for producing energy according to this invention.

FIG. 3 illustrates schematically an alternative embodiment for producing energy according to this invention.

Referring specifically to FIG. 1, the area bounded by lines ABCDA contains the most preferred alloys accord- The alloys having approximately 3,l73,783 Patented Mar. 16, 19%5 the composition of point A have a melting point between about -72 C. and 73 C. Alloys having the approximate composition of points B, C, and D have melting points of about 70 C. Alloys having a composition falling on the lin EFGHE have a melting point of approximately 60 C. Alloys having a composition falling within the area bounded by line EFGHE and outside the area bounded by ABCDA, have a melting point between about 60 C. and about -70 C.

Alloys having the composition of this invention are particularly useful in applications wherein it is necessary to store a heat transfer medium under conditions in which it is undesirable or impossible to maintain the storage receptacle in a heated condition. Such conditions occur in many systems, for example, in aircraft and missile applications.

Referring specifically to FIG. 2, which exemplifies one specific application of the alloys of this invention in producing power, an alkali metal alloy of this invention is withdrawn from a mixed metal storage receptacle 10 through a conduit 12 by pump means 14 and is transferred to a fractionator l6 and thence to a boiler 18. In boiler 18, heat from a source 26 is supplied to the alkali metal alloy of this invention. Heat source 26 can be connected to any heat generating source such as steam or molten sodium from an atomic reactor. The alloy of this invention is heated in boiler 18 to the boiling point of cesium (670 C.) whereupon cesium rich vapor is distilled out of boiler 13 upward into fractiona-tor 16. The residue of cesium-lean sodium and potassium left in boiler 18 is conducted by means of a conduit 20 to a mixer 22.

A cesium vapor stream is conducted from fractionator 16 by means of a conduit 24 to a super heater 25. The cesium vapor is supplied with any additional heat as may be required in the super heater 25. If additional heating is not required, super heater 25 can be omitted. The cesium vapor is then conducted by means of a conduit 28 to a power producing means 30 wherein the cesium vapor expends a portion of its energy in the production of power. Any suitable power producing means including, for example, a turbine can be used to produce power. Conventional turbines known to the art are suitable for this purpose. Cesium vapor is expelled through power producing means 3t) and is conveyed by means of a conduit 32 to a condenser 34 wherein the cesium vapor is condensed to liquid cesium. Any suitable condensing means can be employed at this stage, it only being necessary that the particular condenser be capable of condensing substantially all of the cesium vapor chosen to cesium liquid.

In mixer 22, the liquid residue of sodium and potassium from conduit 20 is mixed with the liquid cesium from conduit 36 to form the alloy of this invention in the mixer 22. The alloy of this invention is then conveyed by means of conduit 38 to receptacle lit for storage prior to reuse in the cycle.

In operating the equipment illustrated by FIG. 2, the rate of liquid residue supplied to mixer 22 through conduit 2t) and the rate of liquid cesium supplied to mixer 22 through conduit 36 are regulated so that the proper proportions of cesium, sodium and potassium are present in mixer 22 to constitute an alloy of this invention.

The compositions of this invention can be employed advantageously in a power producing cycle wherein the composition and its individual constituents are the only heat transfer media employed in the entire power generating system.

One advantageous power generating system in which the compositions of this invention can be employed as the sole heat transfer medium is that illustrated in FIG. 3.

According to the process schematically shown in FIG.

3 3, afractionator 401s supplied by a conduit 42 with a liquid binary alkali metal mixture. of sodium and potassium. This binary mixture --has been heated almost to its boiling point under the pressure of the system by passage The alkali metals used to prepare the alloys of this invention are commercially available. These commercially available alkali metals are of adequate purity for use in this invention.

through atomic reactor44; In .boiler'46, this binary mix- 5 The use of cesium in the production of power by means ture is contacted'with a cesium rich composition supplied of extracting power from cesium vapor has many advanthrough a conduit 48. Fractionator 40 and boiler 46 optages. In many applications such as, for example, high erate to separate the cesium from the sodium and potastemperature nuclear applications, it is necessary to use sium. The cesium leaves thefractionator 40 as a vapor liquidmetals since these are the only materials which are which is conducted through a conduit 50 to a power pro-- adequately stable under these conditions. Alkali metals ducing means 52. In power producing means 52, the are useful in these applications because they have relativeexcess energy contained Within the cesium rich vapor is ly low melting and boiling points and are liquid over wide expended to produce power by a conventional means as, tempenature ranges. For many applications, cesium is for example, a turbine, .a magneto'nydrodynamic generator particularly desirable because of its very low melting point or combinations of these, and the like. Cesium rich vapor of 28.5 C. This low melting point means that when is then conducted through a conduit 54 to a condenser 56 cesium is present in its liquid state, excessive heat need wherein the cesium is condensed to its liquid state. The not be applied to the cesium to keep it liquid. Also, if condensed cesium rich liquid is then returned through a the cesium is inadvertently allowed to solidify in the apconduit'48 and fractionator 40 to boiler 46. Portions or paratus, it can be rendered moltenagain Without the apall of this system can be placed under either positive or plication of large quantities of heat; negative pressure, with respect to atmospheric pressure, Cesium has many desirable physical properties which as is desired to achieve adequate material and energy balmake it valuable for use in the production of power. For ances. example, it has a low density and a low heat of vaporiza- It is necessary to avoid the circulation of any substantion. It is often desirable to operate the power producing tial amount of cesium through an atomic reactor because process of this invention in such a manner that the initial cesium has a relatively high neutron cross section. Soditernary mixture which is supplied to the boiler is someum andpotassium, on the other hand, can be circulated what richer in cesium than those compositions indicated through an atomic reactor without difficulty because they above to be the preferred compositions. When the terpossessrelatively low neutron cross sections. If it is denary mixtures of this invention are heated and tractionsired to use this fluid as a moderator within the reactor, ated to provide cesium vapor for-use in producing power, an amount ofcesium proportional to the amount of modifthe initial starting composition is rich in cesium, the eration desired can be circulated with the sodium and vapor which is evolved from the boiler will be substanpotassillmtially pure cesium. Under these conditions, the residue In the specification, claims and specific examples, all left in the boiler will be a composition which is close to parts and percentages areby weight unless otherwise inthe area defined'by line ABCDA in FIG. 1 andwill thus dicated. enjoy the advantages of a low melting point. In this man- In atypical preparation of the eutectic alloy of this innor, it is possible to optimize both the advantages of usvention, molten cesium, potassium and sodium are mixed ing a substantially pure cesium vapor and developinga under an inert atmosphere of argon to produce an alloy residue with avery low melting point. having the composition, 3.02% sodium, 21.55% potas- 40 The equipment'utilized in the power producing process $i11mand75-43% 7 of this invention can be relatively light-weight because The fOllOWing ta C ins P rtin nt 'EhB m dYIIamiC excessively high pressures are not involved. Furthermore, data comparing the properties of typical alloys of this insince cesium has a comparatively low boiling point, the vention with the properties of sodium, potassium, cesium, temperatures encountered in this process are not such that mercury and various binary mixtures. excessive precautions are necessary to prevent the cesium Table l Na-K-Cs Alloy Point A Pomt B Point H 'Melting Point 0.) 53.7 97.8 28.5, -3s 9 -10. -43 --25 -73.1 09.2 63.8 Boiling Point 0.) 750 3513 705 357 300 733 746 743 747 753 AH vaporization (cal./g.) 496 1,005 46 69 7 613 226 189. 247 264 292 Heat Capacity (caL/g.) 0.189 at 0.31 0.000 0,0323 0.212 0.088 0.07 0. 095 0.10 0.11 200 0 AH Fusion (cal./g.) 14.5 7 0 2.s 17.5 0.23 4. 03 5.3 7.3 3.1 Density (g.lcc.) 0.733 51; 0 s91 (250 1 8(4): 23 13. 1 1 c 0. 75 1. 27 1.80 1.58 1. 53 1. Viscosity (centipoises) 03sii250 90 1.01 200 0.30 0. 30 0.352 0. 310 0.303 0.311 Thermal Conductivity (cal./sec.- 0.10 (300 0.1974 Qi at 0.0303 at 0. 133 0.072 0.080 0. 085 0.087 0. 098

cm.- 0.). 0.). (20 mp 220 0.

Wt. Percent Atom Percent A B H A B H These data show that the alloys of this invention have 70 vapor from attacking the equipment. When a turbine is used as the'power producing means, it is possible to use a turbine having only two stages and a small rotor diameter to absorb the enthalpy drop with cesium. This type of turbine is compact and lightweight which are important advantages in missile, aircraft and spacecraft applications.

The ternary compositions of this invention constitute highly desirable heat transfer media because of their relatively low melting and high boiling points coupled with good heat capacity and thermal-conductivity. The extremely low melting points of these alloys render them particularly desirable for use in applications in which it is impossible or impractical to maintain a heat transfer medium in a heated condition to prevent its solidification. The ternary mixtures of this invention are liquids having substantially constant physical and chemical properties over a temperature range of almost 800 C.

As will be understood by those skilled in the art, What has been described is the preferred embodiment of the invention; however, many modifications, changes and substitutions can be made therein without departing from the scope and the spirit of the following claims.

What is claimed is:

1. An alkali metal alloy consisting essentially of from about 2 to about 7% sodium, from about 16 to about 36% potassium and from about 60 to about 80% cesium.

DAVID L. RECK,

6 2. An alkali metal alloy consisting essentially of from about 2.5 to about 4.5% sodium and from about 20 to about 31% potassium and from about to about 77% cesium.

3. A ternary eutectic alkali metal alloy consisting essentially of about 73% cesium, about 24% potassium and about 3% sodium.

References Cited by the Examiner UNITED STATES PATENTS Primary Examiner. 

1. AN ALKALI METAL ALLOY CONSISTING ESSENTIALLY OF 